Structural chemistry of oxides: Oxygen vacancy dynamics

Atomic vacancies in oxides induce deviations from ideal stoichiometry, critically influencing their functional properties in applications such as energy storage-conversion, catalysis, and electronic devices. The dynamic behavior of these vacancies as main mass transport mediums to exchange chemical species with surroundings under operating conditions is central to oxide redox reactions running with the Mars-van Krevelen (MvK) mechanism; yet in-situ atomic-scale monitoring of the vacancy dynamics and vacancy-induced secondary defects within oxides remains challenging due to both their rapid transport kinetics at buried subsurface/interface and characterization difficulties, arising from the insulating nature of bulk oxides and the spatial-resolution requirement in reaction conditions. These challenges hinder precise defect engineering for the performance optimization of functional oxides. In this review, recent advancements in tracking oxygen vacancy and vacancy-induced secondary defects dynamics in oxides, including surface steps, cation vacancies, interfacial dislocations, ledges, and interfaces, have been summarized. The dynamic interconversion of defects and their synergistic effects on surface/subsurface/interface evolution are mainly discussed. The aim of this review is to enhance understanding of defect dynamics and their pivotal role in modulating structural dynamics and surface reaction reactivity, which is highly relevant to the catalyst activity/selectivity/stability evaluation of functional oxide catalysts for electroreduction and catalytic oxidation reactions. Finally, strategies to control buried subsurface and interfacial defects (interface engineering) through tailored surface reactions are proposed, offering new pathways to customize the performance of advanced oxide-based materials.